As hydrocarbons are burned in internal combustion engines, such as, for example, in a diesel engine or a spark-ignition engine, undesirable byproducts are formed. Some of the undesirable byproducts may be in the form of nitrogen oxides (“NOx”). Selective catalytic reduction (“SCR”) of NOx with reducing agents, such as urea or ammonia for example, is known in industrial applications. In the SCR system, a reducing agent is injected into the flow of exhaust gas before the catalyst. Water in the droplets from the injection solution evaporates, leaving urea behind, which decomposes and hydrolyzes into ammonia. Ammonia is thus produced through the evaporation of the water droplets and urea decomposition. NOx reacts with the ammonia and is catalytically reduced in the presence of ammonia. Thus, a factor in ensuring proper operation of the SCR system is proper decomposition of urea to form adequate amounts of ammonia.